The present invention relates to an apparatus for controlling the quantity of light of a copying apparatus, and more particularly, to an apparatus for controlling the quantity of light to uniformalize the quantity of central light and the quantity of marginal light in a variable power type copying apparatus.
A projection optical system of the copying apparatus has a large angle of view and therefore the quantity of marginal light is usually insufficient. This problem has been solved by increasing the quantity of marginal light and by uniformalizing the brightness of the image plane with the use of an insertable diaphragm or a stop for controlling the quantity of light which is provided with a complicated driving apparatus.
The problem of lack of quantity of marginal light is also found in the variable power type copying apparatus. For example, when uniformalizing the brightness of the image plane by compensating the lack of the quantity of marginal light at a high magnification side according to the method above, it sometimes causes an excess of the quantity of marginal light at a low magnification side and fails to uniformalize the brightness of the image plane.
For correcting the excess of the quantity of marginal light, it is a conventional manner to manually insert a diaphragm member or a stop member for interrupting a part of the quantity of marginal light into the projection optical system. However the inserting operation of the diaphragm member is troublesome and is liable to be forgotten.